I think both of your prices are too low, but if you don't want to change the drop off price I would at least increase the onsite prices. Not sure why you waive the set up fee for larger parties, it's more work. I also hope you're charging something for the additional staff...gratuity, service fee, catering fee, or whatever you want to call it. Otherwise, your staff might be absorbing most of your profits. Keep in mind the time & labor of purchasing, prepping, cooking & packaging…all before the party even starts.
I've tried several types of pricing formats, and now go with an all inclusive price per head, because it works for me. I have different menu packages with add-on availability, and I've simply increased the price by a few bucks to cover everything needed, including a light staff & onsite reheating when possible. I use a smoker trailer, which is great for advertising. My prices are on the higher side (partially b/c of the all inclusive), but I know I put out a great product. Don't sell yourself short...If your BBQ is good, people expect you to charge for it!
Meadow Creek TS-250, BQ Grills Pig Cooker, Weber WSM 22.5"